Photographic elements and process for producing vesicular images

ABSTRACT

A photographic element for producing vesicular images having extended latitudes and low gradations comprising two or more superimposed layers, each comprising a binder material and a photosensitive compound capable of decomposing upon exposure to light to form gas wherein each of said binder materials has a different permeability to gas. A process for producing vesicular images having extended latitudes and low gradations comprising imagewise exposing the above-described photographic elements to light to decompose the photosensitive compounds and heating the element to develop the vesicular images.

United States Patent 3,143,418 8/1964 Priest et al. 96/49 3,215,529 11/1965 Lindquist et al. 96/75 X 3,313,626 4/1967 Whitney 96/68 X 3,353,984 11/1967 Landau 96/75 X 3,370,949 2/1968 Van Groenland 96/75 3,466,172 9/1969 Skarvinko 96/75 3,484,241 12/1969 Evleth et a] 96/75 X 3,498,786 3/1970 Notley et al. 96/49 X OTHER REFERENCES Skarvinko; E. R., IBM Tech. Disc. Bulletin," Vol. 9, N0. 10. Pp. 1378-1379,Mar.27, 1967 Primary Examiner-.1. Travis Brown Assistant Examiner-Charles L. Bowers. Jr. Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak VlSUAL PROrECTION DENSITY 0F OPV [72] Inventor Eugene R. Skarvinko Binghamton, N.Y. [21] Appl. No. 713,002 [22] Filed Mar. 14, 1968 [45] Patented Oct. 26, 1971 [73] Assignee International Business Machines Corporation Armonk, N.Y.

[54] PHOTOGRAPHIC ELEMENTS AND PROCESS FOR PRODUCING VESICULAR IMAGES 16 Claims, 1 Drawing Fig.

[52] US. Cl 96/41, 96/49, 96/27, 96/68, 96/75, 96/91 [51] Int. Cl G03c 5/04, G03c 5/18, G03c1/54 [50] Field of Search 96/49, 75, 91, 48. 27, 68, 41

[56] References Cited UNITED STATES PATENTS 3,515,547 6/1970 Allentoff et al 96/75 X 2,501,874 3/1950 Peterson 96/75 X 3,032,414 5/1962 James et al. 96/75 X 3,069,268 12/1962 Herrick 96/75 X 3,141,773 7/1964 Hellmig 96/68 VISUAL PROJECTION DENSITY 0F ORIGINAL PATENTEDnm 2s IQYI 3.615.475

VISUAL PROJECTION DENSITY OF COPY VISUAL PROJECTION DENSITY OF ORIGINAL VW O By 52 6 wh /4mg Z471.

ATTORNEYS PHOTOGRAPIIIC ELEMENTS AND PROCESS FOR PRODUCING VESICULAR IMAGES BACKGROUND OF THE INVENTION Vesicular images comprise patterns of small bubbles or vesi- ,cles of gas entrapped in photographic film materials. This background substrate to impart contrast to the image or where the image is projected onto a screen, an image corresponding to the vesicular image is produced. The optical density of that image, either as reproduced or as it appears in the film itself, is dependent on the number and size of the vesicular bubbles and their proximity to each other.

Vesicular photographic materials have found only limited use in the prior art, however, due to the high gradation associated with conventional vesicular images. Thus, the prior art vesicular images have high contrast between the black and white areas of the developed film thereby rendering them unsuitable for copying continuous tone images such as X-ray transparencies, for example. As a result, vesicular photographic materials have found primary application only in line 'copy work, etc.

Stated differently, when exposing vesicular photographic materials through masters, transparencies, etc. vesicles or bubbles form wherever the light strikes the photographic layerJNobubbles form in the unexposed areas of the film. It is "a characteristic of vesicular photographic materials that the degree of bubble formation and, hence, the contrast between the light and dark areas of the resulting image is not subject to rigorous control. Consequently, where the original imageto be reproduced contains gray or varying shades between black and white, these gray areas cannot be faithfully reproduced. The resulting copy will reproduce these gray areas as either black or white, depending upon the amount of light transmitted through these gray areas to the photographic film during the exposure. Thus, the vesicular images produced in the prior art are said to have a short gray scale.

Various attempts have been made in the prior art to reduce the contrast or gamma of vesicular images, thereby extending the gray scale of the reproduction.

U.S. Pat. No. 2,703,756 to Herrick et a1. discloses adjusting the sensitometric characteristics of vesicular images, i.e., reducing the contrast or gamma, of vesicular image-forming layers by dispersing a light sensitive diazonium compound in a binder comprising a'mixture of a thermoplastic, hydrophobic resin and a water soluble gas impermeable organic colloid. It is disclosed that the gradation of the resulting developed image can be adjusted by varying the ratio of colloid to hydrophobic resin.

U.S. Pat. No. 3,149,971 to Baril et al. discloses a process for decreasing photographic gamma and increasing photographic speed by treatment of the vesicular photographic material with a heated aqueous fluid prior to exposure and development.

While all of these methods have the effect of improving the sensitometric characteristics of vesicular photographic materials as to a particular shade or tone desired to be reproduced, none are sufficiently effective to render such materials suitable for the reproduction of continuous tone images containing varying shades or tones.

It is an object of the present invention to provide vesicular photographic elements and processes for the production of high-quality vesicular images having extended latitudes and lower gradations than heretofore possible.

It is a further object of the invention to provide vesicular photographic materials and processes for the production of vesicular images having improved sensitometric characteristics such that the gray scale" of the reproduced image is substantially lengthened over that heretofore possible.

It is a further object of the invention to reduce the contrast or gamma of vesicular images.

It is a further object of the present invention to provide vesicular photographic materials and V processes for the production of vesicular images especially adapted for the faithful reproduction of continuous tone images such as X-ray transparencies, etc.

It is a further object of the inventionto provide vesicular photographic materials and processes for the production of vesicular images especially adapted for the faithful reproduction of continuous tone images containing varying shades or tones.

BRIEF DESCRIPTION OF INVENTION bility to gas and aphotosensitive compound capable of decomposing upon exposure to light to form gas and wherein each binder material has a different permeability to gas.

The above objects are further realized by the present invention which provides a process for the production of vesicular images comprising exposing the above described photographic elements .to light to decompose the photosensitive compounds and form gas and heating the element to develop a vesicular image comprising tiny bubbles or vesicles of the gas.

The photographic elements and the process of the present invention operate ,to provide vesicular images in each of the superimposedlayers, each corresponding to a different shade or tone in the original image. By incorporating a different binder material in each of the superimposed layers having different permeabilities to the entrapped vesicular gas, each layer will provide a vesicular image having different sensitometric characteristics or different gradations and tones. The overall effect of this is that an original image can be exactly reproduced as to its varying shades and tones. This results in an extension of the latitude of the reproduced image over that heretofore possible.

By making each layer sensitive to differing intensities of light by varying the gas permeability of the binder material, the original image is exactly reproduced as a lamination of partial images.

Asingle layer cannot be made sufliciently sensitive to varying light intensities due to-the fact that each binder has a fixed characteristic gas permeability. If a vesicular photographic element were provided wherein the binder material had a rela tively high permeability to gas, lower contrast would be obtained, however, the maximum obtainable density of the resulting image would be reduced thereby shortening the density range. By the'present invention, however, although the density range is shortened in those layers wherein the contrast is lowered,-the loss in density is regained so to speak in those layers wherein the contrast is high due to the employment of a binder material having a difierent permeability to gas.

DETAILED. DESCRIPTION OF THE DRAWING The accompanying drawing illustrates the improvement of the sensitometric characteristics of vesicular photographic materials provided by the present invention.

Curve A represents the sensitometric properties of the improved vesicular film of theinvention prepared in the Example hereinbelow in terms of the visual projection density ofjthe copied image as compared with the visual projection density of the original. Curve B represents the sensitometric properties of a typical one layer prior art vesicular film. More specifically,the prior art film utilized was Kalvar type 10 whichcomprises a photosensitive diazonium compound dispersed in a polyvinylidene chloride binder and supported on a polyester support.

It should be noted that Curve A has a lower slope than the steeper Curve B, thereby indicating lower gradation in the copied image employing the vesicular film of the invention. As noted above, a lower gradation indicates better reproducibility of the varying shades and tones of an original. Stated differently, the vesicular film of the invention has a longer gray scale than that of the prior art.

DETAILED DESCRIPTION OF THE INVENTION Any of the well-known photosensitive compounds may be employed to form the vesicular images. The only criterion is that the compound be sensitive to a certain wavelength of light such that it decomposes upon exposure to that light to form a gas. The most common of these materials are the so-called diazonium salts, however, it is to be understood that any photosensitive compound capable of decomposing upon exposure to light to form gas may be employed.

Suitable photosensitive materials are the metallic double salts of the p-diazo-dialkylanilines such as the zinc chloride salts of p-diazo-dimethylaniline, p-diazo-diethylaniline, pdiazo-ethylhydroxyethylaniline, p-diazo-ethylmethylaniline, p-diazo-diethylmethylaniline, etc.

Substances liberating carbon oxides upon exposure to light include various iron salts in admixture with organic acids such as a mixture of ferric ammonium citrate and oxalic acid.

Generally, any of the photosensitive compounds described in U.S. Pat. Nos. 3,093,478 to Peterson, that 3,251,690 to Parker et al., and 3,260,599 to Lokken may be employed.

It is also to be understood that a different photosensitive compound may be incorporated in each of the various layers of the photographic element of the present invention.

While a different binder entity may be employed in each layer it is preferred to employ similar synthetic resin mixtures in each layer wherein the proportions of resin in each layer are varied to provide different gas permeabilities.

This technique is preferred due to the greater degree of control it affords over the ratio of gas permeabilities between the various layers. Thus, by changing only slightly the ratio of resin ingredients from layer to layer, the gas permeabilities are likewise changed only slightly.

Among the resins which may be employed either singly or as mixture are cellulose derivatives such as cellulose acetate, cellulose propionate, ethyl cellulose, etc., vinyl resins such as polyvinyl chloride, polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate, copolymers of acrylonitrile and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinyl chloride and methyl acrylate or acrylic acid, copolymers of vinyl acetate and diethyl maleate, polyvinyl alcohol, etc., styrene resins such as polystyrene, polystyrene-isobutylene, copolymers of styrene, vinylidene fluoride and l,1-difluoroethylene, etc., polyacrylates such as the polyalkyl acrylates and the polyalkyl methacrylates such as polymethyl acylate,polymethyl methacrylate, polyethyl acrylate, polybutyl methacrylate, etc., polyamides; phenolic resins, polyvinyl pyrrolidone, etc.

These binder materials may be employed in preparing the photographic elements of the present invention in the form of latexes, aqueous dispersions, plastisols, organosols and solutions in organic solvents. The resins may be mixed in any conventional manner and coated according to any of the wellknown prior art methods.

Generally, the photosensitive compound is dissolved in a suitable solvent and combined with a solution or dispersion of the binder and coated on a suitable photographic support. It is to be understood, however, that any conventional and well known method for preparing vesicular image forming elements may be used to prepare the elements of the present invention.

The support substrate may be any transparent or opaque material such as paper, polyethylene terephthalate, cellulose acetate, etc.

Optionally, a nonsupported element may be prepared by separately extruding the various layers and adhering them together or by coating each individual layer on a temporary substrate and subsequently removing the latter.

The particular binder and number of layers in each particular instance will depend upon the degree of sensitometric characteristic control desired in each case. By providing a relatively large number of layers, each differing only slightly in gas permeability from the others, a high degree of half tone control may be achieved. It has been found, however, that the provision of only two layers provides images of extended latitude and low gradation thereby enabling a high degree of half tone control heretofore impossible. It is to be understood, however, that any number of layers employing any desired number of different binders may be employed in any particular instance so long as the gas permeabilities of the binder material in each layer differ.

Moreover, the rigidity or hardness of each of the various layers may be altered to conform to desired applications. If a nonsupported material is desired, a rigid, hard binder material must be employed. Where the material is to be deposited on a support, it may be softer and more flexible.

Gas permeabilities of binders are generally measured according to methods well known in the prior art (c.f. U.S. Pat. No. 3,149,971 and Light-Sensitive systems", Jaromir Kosar, Wiley et al., Page 277). The gas permeability is usually expressed as gas constant defined as the number of cubic centimeters of gas transmitted by an area of one square centimeter in one second at 30 C. when the pressure gradient is one centimeter of mercury at one centimeter of thickness.

Gas permeabilities of binders are generally measured according to methods well known in the prior art, for example, according to the process set forth in U.S. Pat. No. 3,149,971.

Generally, the particular gas permeabilities of the various binders employed herein are not critical, it only being necessary that the gas permeability constant difi'er from layer to layer. It will be understood that the two differences in permeability constants from layer to layer will depend on the particular image desired to be reproduced.

The larger the number of varying shades in the original and the lesser the contrast between these shades, the smaller the differences in gas constants between the various layers will be required.

Smaller numbers of shades and the greater contrasts therebetween will require larger gas constant differences.

Generally, binders having gas constants ranging from about 8.6Xl0" (cm. cm. sec."(cm. I-lg./cm.)] to about 8X10 [cm. cm. sec. (cm. Hg./cm.)] may be employed.

It is to be understood. that any of the conventional plasticizers, fillers, pigments, etc. may be included in the binder materials of the present invention.

In a preferred embodiment, a photographic support layer is coated with a first layer comprising a photosensitive diazonium salt dispersed in a resin mixture comprising from about 22 percent to about 26 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 8 percent to about 15 percent of a polyacrylate such as polymethylacrylate. This layer is then overcoated with a second layer comprising a photosensitive diazonium compound dispersed in a resin mixture comprising from about 12 percent to about 15 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 12 percent to about 15 percent of polyacrylate. The difference in gas permeability between these two binder materials enables a high degree of half tone control and the production of vesicular images having extended latitude and low gradation and a consequent extension of the gray scale."

According to a further embodiment of the invention, the multilayered photographic elements are preliminarily thermally treated prior to exposure and development. The effect of this thermal treatment is to increase the photographic speed of only the uppermost layer without affecting the underlying layers, thereby further extending the latitude of the resulting image.

This thermal treatment may take the form of any process of applying heat to a filmlike material. Temperatures up to about 100 C. may be employed. According to a preferred embodiment, the photographic elements are subjected to hotor boiling water or to steam.

The invention will be further illustrated by the. following nonlimiting examples.

EXAMPLE 1 A first coating composition was prepared according to the following formulation.

% by weight p-diazo-dimethyl aniline zinc chloride salt -9 Dow Saran F-220 (vinylidene chlonde-acrylonitrile copolymer) Rohm & Haas Acryloid 101 (mixture of polymer" of esters of acrylic and 81 methacrylic acids) liethylethyl ketone Acetonitrile by weight p-diazo-dimethyl aniline zinc chloride salt 2.44 Saran OX2 l 2 (vinylidene chloride acrylonitrile copolymer) '4 22 Acryloid lOl |4.22 Methylethyl ketone 39.90 Methylalcohol i3 30 Acetrontrile I568 Hycar I432 lB.F Goodrich Chemical Co butadieneacrylonitrile copolymer) (plasticerizer) 25 The above ingredients are prepared in the same manner as the first coating composition and coated over the first layer and dried and cured in the same manner to give a second coating having a thickness of about 0.3 mil.

The finished element is then treated in a 1 percent aqueous solution of Tergitol NP35 wetting agent for 20 seconds at 200 F.

The finished element was tested by exposing the film strip in a sensitometer containing a 100 watt G.E. mercury lamp for 26 seconds. The visual projection density of the resulting image was measured and plotted against the visual projection density of the original. See curve A of the accompanying drawing.

As is apparent from the drawing, this curve shows increased latitude and lower gradation far superior to that of the prior art vesicular image.

What is claimed is:

l. A photographic vesicular-image-forming element capable of yielding continuous tone vesicular images of extended latitude and low gradation comprising a plurality of superimposed, contiguous vesicular-image-yielding layers, each of' said layers comprising (1) a mixture of water insoluble, synthetic thermoplastic resins as binder material, said material having a low permeability to gas, wherein in each layer the ratio of the amounts of saidresins present as the binder material is different such that the permeability to said gas of said binder material is different in each of said layers,;and (2) a photosensitive compound capable of decomposing upon exposure to light to form gas, wherein the binder material of each of said layers has a different permeability to said gas resulting from the decomposition of said photosensitive compound, each of said layersproviding a vesicular image upon decomposition of said photosensitive compound and development to form said image, said image corresponding to the varying tone of the original image being reproduced, whereby said original image is reproduced as a lamination of partial images in the said layers.

2. A photographic vesicular-image-forming element capable of yielding continuous tone vesicular images of extended latitude and.low gradation comprising (1) a support coated with (2) a first vesicular-image-yielding layer comprising a photosensitive compound capable-of decomposing upon expo? sure to light to form gas, and'a mixture of water-insoluble,;:j

synthetic thermoplastic resins as binder material which has.

low permeability to gas different from that of said binder material of said first layer, wherein in each layer the ratio of the amounts of said resins present as the binder material is dif-- ferent such that the permeability to said gas is different in each of said layers, each of said layers providing a vesicular image upon decomposition of said photosensitive compound and developmentto formsaid image which corresponds to the varying tone of the original image being reproduced, whereby said original image is reproduced as a lamination of partial images in the said layers. v

3. The element of claim 1 wherein said plurality of superimposed layers are coated on a support.

4. The element of claim l wherein said photosensitive compound is a diazonium compound which decomposes upon exposure to light to form nitrogen gas.

5. The element of claim 4 wherein said diazonium compound is a p-diazo-dialkylaniline salt.

6. The element of claim 5 wherein said diazonium compound is the zinc chloride saltof p-diazo-dimethylaniline.

7. The element of claim 2 wherein said binder materials have a gasconstant within the range of from about 8.6 X 10 8. A photographic vesicular-image-forming element as claimed iri claim 1 wherein the binder material of one layer comprises from about 22 percent to about 26 percent of a copolymer of vinylidene chloride and acrylonitrile and'from about 8 percent to about 15 percent of polyacrylate, and the binder material of a different layer comprises from about 12 percent to about 15 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 12 percent to about 15 percent of a polyacrylate.

9. A method of preparing vesicular images having extended latitudes and lower gradations comprising imagewise exposing the element of claim- 1 to light to thereby decompose the photosensitive compounds under areas exposed to light,

the photosensitive compounds under areas exposed to light, thereby resulting in the production of gas from said photosensitive compounds, and thereafter heating the element to develop a vesicular image from the gas resulting from the decomposition of said photosensitive compounds.

11. A method according to claim 10 including the step of preliminarily heating said element, at a sufficiently low temperature to prevent vesicular image formation, prior to said exposing step to improve the photographic speed and tone reproduction of only said first layer.

12. A method according to claim 11 wherein said heating step is accomplished by contacting said element with a member selected from the group consisting of hot water and steam.

13. The element of claim 2 wherein said photosensitive compound is a diazonium compound which decomposes upon exposure to light to form nitrogen.

14. The element of claim 2 wherein said binder materials have a gas constant within the range of from about 8.6X10 [cm. cm. sec. (cm. Hg./cm.)"] to about 8X10 [cm. cm. sec. (cm. Hg./cm.].

15. The element of claim 2 wherein said binder material is selected from the group consisting of cellulose acetate, cellulose propionate, ethyl cellulose, polyvinyl chloride, polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate, copolymers of acrylonitrile and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinyl chloride and a member selected from the group consisting of methyl acrylate and acrylic acid, copolymers of vinyl acetate and a member selected from the group consisting of diethyl maleate and polyvinyl alcohol, polystyrene, polystyrene-isobutylene, copolymers of styrene, vinylidene fluoride and l,l-difluoroethylene, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl methacrylate, polyamides, phenolic resins, polyvinyl pyrrolidone, and mixtures thereof.

16. A photographic vesicular-image-yielding element as claimed in claim 1, wherein the binder material of said first layer comprises from about 22 percent to about 26 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 8 percent to about 15 percent of a polyacrylate, and the binder material of said second layer comprises from about 12 percent to about 15 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 12 percent to about 15 percent of a polyacrylate.

Patent No. 3,615,475 Dated October 26, 1971 Inventor(s) Eugene R- SkarVlnkO It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, Line 32 delete "that" after "Peterson" Line 59 "acylate" should be "acrylate" Column 4, Line 31 "a" has been deleted between "as" and "gas" Line 52"53 "8.6)(10 [cm. cmg sec, 11

(cm. Hg./cm. to about 8 X 10 [cm. 3 m. see. (cm.Hg./cm-

should be (cm Hg/cm) 8.6 x 10 [cm cm Column 5, Line 5 "filmlike" should be "film-like" Line 24 "polymer should be "polymers" Line 37 No space between "10" and "minutes" Line 54 "25" should be ".25"

Column 6, Line 28 "Yeilding" should be"Yielding" IORM pO o5 0'69, USCOMM-DC B0376-P69 U 5. GOVEINHENY Ilnnmu orncr nu n-un-un Patent No. 3,615 ,475 Dated October 26 1971 Inventm-(S) Eugene R. Skarvinko PAGE 2 -It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page 2. Cont.

Colum 6, Line 53,54,55 "8.6 x 10 [cm. cm. sec.

(Claim 7) 11 (cm. Hg./Cmto about 3 l2 8 x 10 [cm. cm. sec. q-/ should be -2 -l 8.6 x l0 16 [cm cm sec -1 (cm Hg/cm) 1 to about 8 x l0 l0 -l [cm Cm sec: 1 (cm Hg/cm) 1 Claim 7 should be dependent from Claim 1.

columrll 6 Line 60 "a" has been deleted between (clalm 8) "of"and "polyacrylate" Column 7 Lines 19 20 ,2]. 116 3 12 ll (Claim 14) "8. 6 x 10 [cm.

ll (cm. Hg./cm. to about (Cm- Hg./cm. should be pomsu (10459} USCOMM-DC soavemse US GOVERNHENY PRINTING OFF'CE '9" 0-15").

Patent No. Dated October 26, 71

Inventor-(S) Eugene R. Skarvinko PAGE 3 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page 3 Cont.

Column 7 Lines 19, 20, 21 3 (Claim 14) 8.6 x 10 [cm m sec g/ l to about 8 x 10 cm sec (cm Hg/cm) Si ned and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents P0405) uo'sgl USCOMM-DC eons-M9 US, GDVEINMIIIT PRINTING OFFICE I969 0-36i-334 

2. A photographic vesicular-image-forming element capable of yielding continuous tone vesicular images of extended latitude and low gradation comprising (1) a support coated with (2) a first vesicular-image-yielding layer comprising a photosensitive compound capable of decomposing upon exposure to light to form gas, and a mixture of water-insoluble, synthetic thermoplastic resins as binder material, said material having a low permeability to said gas, and (3) a second vesicular-image-yeilding layer coated on said first layer comprising a photosensitive compound capable of decomposing upon exposure to light to form gas and a mixture of water-insoluble, synthetic thermoplastic resins as binder material which has low permeability to gas different from that of said binder material of said first layer, wherein in each layer the ratio of the amounts of said resins present as the binder material is different such that the permeability to said gas is different in each of said layers, each of said layers providing a vesicular image upon decomposition of said photosensitive compound and development to form said image which corresponds to the varying tone of the original image being reproduced, whereby said original image is reproduced as a lamination of partial images in the said layers.
 3. The element of claim 1 wherein said plurality of superimposed layers are coated on a support.
 4. The element of claim 1 wherein said photosensitive compound is a diazonium compound which decomposes upon exposure to light to form nitrogen gas.
 5. The element of claim 4 wherein said diazonium compound is a p-diazo-dialkylanilIne salt.
 6. The element of claim 1 wherein said diazonium compound is the zinc chloride salt of p-diazo-dimethylaniline.
 7. The element of claim 2 wherein said binder materials have a gas constant within the range of from about 8.6 X 10 16 (cm.3 cm. 2 sec. 1 (cm. Hg./cm.) 1) to about 8 X 10 10 (cm.3 cm. 2 sec. 1 (cm. Hg./cm.) 1).
 8. A photographic vesicular-image-forming element as claimed in claim 1 wherein the binder material of one layer comprises from about 22 percent to about 26 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 8 percent to about 15 percent of polyacrylate, and the binder material of a different layer comprises from about 12 percent to about 15 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 12 percent to about 15 percent of a polyacrylate.
 9. A method of preparing vesicular images having extended latitudes and lower gradations comprising imagewise exposing the element of claim 1 to light to thereby decompose the photosensitive compounds under areas exposed to light, thereby resulting in the production of gas from said photosensitive compounds, and thereafter heating the element to develop a vesicular image from the gas resulting from the decomposition of said photosensitive compounds.
 10. A method of preparing vesicular images having extended latitudes and low gradations comprising imagewise exposing the element of claim 2 to light to thereby decompose the photosensitive compounds under areas exposed to light, thereby resulting in the production of gas from said photosensitive compounds, and thereafter heating the element to develop a vesicular image from the gas resulting from the decomposition of said photosensitive compounds.
 11. A method according to claim 10 including the step of preliminarily heating said element, at a sufficiently low temperature to prevent vesicular image formation, prior to said exposing step to improve the photographic speed and tone reproduction of only said first layer.
 12. A method according to claim 11 wherein said heating step is accomplished by contacting said element with a member selected from the group consisting of hot water and steam.
 13. The element of claim 2 wherein said photosensitive compound is a diazonium compound which decomposes upon exposure to light to form nitrogen.
 14. The element of claim 2 wherein said binder materials have a gas constant within the range of from about 8.6 X 10 16 (cm.3 cm. 2 sec. 1 (cm. Hg./cm.) 1) to about 8 X 10 10 (cm.3 cm. 2 sec. 1 (cm. Hg./cm. 1).
 15. The element of claim 2 wherein said binder material is selected from the group consisting of cellulose acetate, cellulose propionate, ethyl cellulose, polyvinyl chloride, polyvinyl acetate, copolymers of vinyl chloride and vinyl acetate, copolymers of acrylonitrile and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinyl chloride and a member selected from the group consisting of methyl acrylate and acrylic acid, copolymers of vinyl acetate and a member selected from the group consisting of diethyl maleate and polyvinyl alcohol, polystyrene, polystyrene-isobutylene, copolymers of styrene, vinylidene fluoride and 1,1-difluoroethylene, polymethyl acrylate, polymethyl methacrylate, polyethyl acrylate, polybutyl methacrylate, polyamides, phenolic resins, polyvinyl pyrrolidone, and mixtures thereof.
 16. A photographic vesicular-image-yielding element as claimed in claim 1, wherein the binder material of said first layer comprises from about 22 percent to about 26 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 8 percent tO about 15 percent of a polyacrylate, and the binder material of said second layer comprises from about 12 percent to about 15 percent of a copolymer of vinylidene chloride and acrylonitrile and from about 12 percent to about 15 percent of a polyacrylate. 